Far right, nationalist groups All-Polish Youth (Młodzież Wszechpolska) and National-Radical Camp (Obóz Narodowo-Radykalny) are being opposed by the left wing November 11 Agreement and other groups.

16.01: Nationalists from the Czech Republic and Serbia are said to be among the far-right demonstrators and buses from Germany and Belgium are thought to have brought in left wing protesters.

Around 4 pm the left wing groups had blocked in nationalists on either side of Plac Konstytucji with police trying to keep the sides apart.

16.10: Spokesperson for Warsaw's ambulance service Marek Niemirski has reported that 10 people have already been injured in the clashes.

Video of a press photographer being attacked by demonstrators is circulating on the internet.

16.15: Police say they earlier detained around 100 protesters outside a left wing centre on the corners of streets Nowy Świat and ul. Świętokrzyskiej.

"Police urge demonstrators to remain calm. Any violation of the law will be severely punished," says police HQ spokesman Mariusz Sokolowski. (PAP)

16.35:Nationalist demonstrators, unable to march their intended route, have turned south down ulica Spacerowa in an attempt to reach the centre of town again via ulica Belwederska. One eye witness has told thenews.pl that 'thousands' of nationalists are being kept an eye on by a police helicopter and are being escorted by police with riot shields. That route will take them past the Belweder Palace, home to President Komorowski, and will later pass the Prime Minister's Office.

16.45:Police have ordered via megaphones that the left wing protesters currently occupying Plac Konstytucji must disperse otherwise they will declare their protest illegal.

16.55:Clashes with police have been reported in the centre of town on ulica Emili Plater. The demonstrators, who appear to be from nationalist groups, were wearing either the white and red of Poland's national flag or football scarves, and threw stones and other objects at the police, reports Polish Radio's IAR news agency.

17.01:The TVN 24 news station is saying that one of its cameramen has been attacked.

17.10: Film uploaded on to youtube is emerging of scenes earlier at Plac Konstytucji. See here.

Earlier there were more peaceful celebrations of Independence Day, with a traditional march by soldiers wearing period uniforms. See here.

Poland regained her independence in 1918 after over 100 years of partitions.

17.23: Roman Kurkiewicz from the left wing 11 November Agreement says that they have achieved their aim of blocking the nationalists' route earlier.

"Our goal has been achieved. The March of Independence, organized by neo-fascists, did not pass through the center of Warsaw, as they intended,” he told the PAP news agency.

Kurkiewicz claims that 'neo-fascists' repeatedly tried to attack them and tried to break into the middle of their demonstration, but police kept them from doing so.

17.34: It is being reported that at around 5 pm, by the statue of inter-war nationalist leader Roman Dmowski, a transmission van owned by the TVN broadcaster was attacked and set on fire. Polish Radio reporters say their car has also been vandalised. Nationalists would have passed that point as they walked back to the centre of town up ul. Belwederska (as reported here at 16.35).

17.55: Prime Minister Donald Tusk is being kept informed of the situation and will recommend severe punishment in the courts for those who take part in violent protest, says the PM's spokesman Pawel Gras.

"It will definitely be the recommendation of the Prime Minister to punish those arrested ruthlessly, regardless of nationality or political sympathies,” he said.

He added the premier is in contact with justice and interior ministers and the Chief of Police.

18.05: Far-right National Revival of Poland (Narodowe Odrodzenie Polski) is marching through the streets of Wroclaw in the south west of the country. The PAP news agency says that around 600 members of the nationalist group are marching to the statue of Boleslaw the Brave. The march has so far been peaceful.

Football supporters are also in the centre of Wroclaw for the Poland versus Italy friendly tonight.

18.20: Twenty one people have been taken to hospital following the violence, says ambulance service spokesman Marek Niemirski.

Some of the injuries come from violence at plac Na Rozdrożu, by the Roman Dmowski statue, as mentioned earlier.

18.35: Police spokesman Mariusz Sokolowski says that they have detained 150 people so far in Warsaw on rioting charges. Eight police officers have been injured. Sokolowski says that police video evidence will be vital in identifying culprits. (PAP)

18.47: President Bronislaw Komorowski is to meet with advisers on whether to consider recommending changes to the current law governing the organization of demonstration and assembly, says his spokeswoman Joanna Trzaska-Wieczorek.

She said the head of state is in favour of giving local authorities more power in being able to decide on the organisation of the marches. She also informed that President Komorowski will not now be attending the Independence Day gala at the Philharmonic Hall tonight, though First Lady Anna may still attend. (PAP)

18.54: President of one of the nationalist groups, All-Polish Youth, Robert Winnicki, says that his march was infiltrated by “masked persons”.

“Unfortunately, the police did not protect the march,” he says and that “provocateurs” aimed to ruin his demonstration.

19.06: Well, the constant buzzing of helicopters overhead has stopped and the news wires have slowed down a little, so that's enough from me today: we will be reporting on the aftermath of the violence on Independence Day on Saturday.